Forage harvesters are machines which chop crop gathered from a field into small pieces to produce animal feed. In the case of crops such as grass or alfalfa, these may have been mown and left to dry in the sun, so that the crop need only be gathered by the harvester. With other crops, such as maize, the forage harvester is also required to cut the crop. Thus, the harvesters may be fitted with different headers to suit the crop being harvested.
The crop, whether cut maize or gathered grass, is fed to a rotating knife drum or cutter which comminutes the product. With grass crops, this alone is sufficient to produce the desired forage. However, when harvesting maize for silage purposes, the cutting alone does not suffice due to the presence of kernels in the crop. The kernels need to be cracked in order to release the nutrient, as uncracked kernels are hard for animals to digest. As cutting alone is insufficient to crack all the kernels, the crop is additionally passed through a crop processor which comprises two closely adjacent rollers, typically having serrated surfaces, which rotate such that there is a speed differential between the adjacent surfaces. The gap between the rollers is set to suit the size of grain passing through and the speed, rotational energy of the rollers, relative movement and serration of the surfaces together ensure cracking of any kernels that are still intact after chopping by the cutter.
The momentum of the maize from the crop processor or the grass from the cutter, as the case may be, carries the crop into a blower which then propels it up a tower to a discharge spout through which it is discharged into a wagon or a trailer drawn by a separate vehicle driven alongside the harvester.
When chopping kernel-free crops, such as grass or alfalfa, the crop processor is not required and leaving it in place in the crop flow path results in its rollers being unnecessarily subjected to wear. To avoid such wear, it has previously been proposed in GB 2 414 373 to pivot the crop processor away from its operative position in the crop path but to leave it on the vehicle in an inoperative position. In order to optimize crop flow, the blower and the crop processor are connected to a common pivot frame so that as the crop processor is withdrawn from the crop flow path, the blower moves downwards to take its place.
Because the drive pulley of the blower needs to move between two different positions, a movable tensioning roller is required for the belt that transmits drive from the engine to the blower. Such a belt, which travels endlessly around a drive pulley and at least one driven pulley, is often very long since the centre distances between the driving and driven pulleys are relatively great. When the machine travels over uneven surfaces, the drive and driven shafts may twist relatively to one another because of frame deformation and cause lateral forces on the belt. These lateral forces may result in the displacement of the belt on the pulleys and even a complete run-off of the belt from the system. Furthermore, if a quick turn is needed, the driver will push the left or right brake and the back of the machine will spin around its front wheels. The large and heavy belt is not always able to follow the quick movement of the back of the machine due to the inertia of the belt. The belt will thus arrive at the tensioning roller under an angle and may run-off.
U.S. Pat. No. 5,242,331 B describes a belt drive system which prevents lateral slippage of the belt in the event that the drive and driven shafts twist relative to one another. This system comprises a tensioning unit having a profiled idler pulley, followed in the belt travel direction by a back chucking roller. The pulley and the roller are mounted at a small distance from each other into a U-shaped retainer to form the tensioning unit. The shaft of the roller is pivotably connected to an arm, which in turn is pivotably connected to the shaft of the driven pulley. Consequently, the distance between the roller and driven pulley is defined. The belt is held between the roller and the idler pulley, such that its sections cannot leave the grooves of the idler pulley.
A disadvantage of this system is that the complete tensioning system, including the adjacent wheel needs to be disassembled before the belt can be removed or replaced. After installation of the new belt, the clamping unit and the retainer need to be re-adjusted so that the belt is correctly aligned and will not run-off. Disassembling and reinstalling the front wheel and the tensioning system and re-adjusting the clamping unit and retainer are critical and time consuming tasks.
In addition thereto, the belt of the drive described in U.S. Pat. No. 5,242,331 has a reduced lifetime since it is subject to excessive wear. The tensioning roller and the idler pulley are retained at a fixed distance from one another in the retainer. A compression spring cylinder is rigidly joined to the retainer to keep the belt under a constant load. However, due to vibrations, the belt will also tend to vibrate and the compression spring cylinder will react to keep a constant pressure on the belt. Because the compression spring cylinder acts directly on the upper portion of the retainer adjacent the back chucking roller, the latter will be pushed more to the front more rigorously than to the idler pulley. This will result in a pinching action of the back chucking roller and idler pulley on the belt. These extra forces push the profiles of the idler pulley deeper into the belt and damage the belt which will result in a reduced lifetime.
Finally, another disadvantage of the system as described in the aforementioned US patent is that the lubrication of the bearings of the back chucking roller and the idler pulley is only possible when the machine is not working. When servicing to the machine, grease is also pumped manually through the lubrication fittings into the interior of the back chucking roller and the idler pulley. This again is a time consuming task and inadequate lubrication of the back chucking roller and the idler pulley will decrease the lifetime of the roller and pulley.